the coin is gone from the sending wallet yet never arrived in the receiving wallet.
Although we often say (or write) that coins are stored in wallets, it is important to remember this is just a convenient shorthand analogy for communication between people.
In reality, Bitcoins don't exist in wallets, they are not stored in wallets and are not moved in and out of or between wallets. Bitcoins don't really travel between wallets and the dont really get sent by one wallet or arrive in another. That's all just handwaving and very loose analogy.
Furthermore, Bitcoins are not stored in the blockchain. The blockchain just keeps a list (a journal) of transactions involving amounts of money using Bitcoin as a unit of measure.
To summarize, whatever the blockchain says happened is what really happened. After about six confirmations it is very unlikely the blockchain will change it's view on this. If someones wallet disagrees with the general and established consensus view of the blockchain, the wallet is wrong. Possibly because the wallet is not synchronized. In theory it may be the receiving-address was wrongly entered - but this is relatively unlikely.
Lets say you went into a shop and took a $20 banknote out of your wallet and handed it to the shopkeeper who put it into his wallet. Then the shopkeeper denies receiving your $20. What do you do then? If you are lucky there is a witness. The witness can't resolve your dispute, you have to take that to a court of law and ask the witness to testify.
The blockchain is simply your witness. The blockchain can produce evidence but it can't resolve a dispute.
the transaction is still missing.
If it is in the blockchain it isn't missing.
If it isn't in the blockchain, you still have the money.
Your transaction is in the blockchain and, at time of writing, has 328 confirmations. 6 confirmations is usually taken as certain. It is as certain as it is possible to be. It is definitely not missing. Waiting will not make it significantly more concrete, more visible or more indisputable. There is no chance of it disappearing (short of unprecedented disaster and the possible end of the Bitcoin world)